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Within data modelling, cardinality is the numerical relationship between rows of one table and rows in another. Common cardinalities include one-to-one , one-to-many , and many-to-many . Cardinality can be used to define data models as well as analyze entities within datasets.
The more general case of partition matroids corresponds to categorized cardinality constraints. These problems are described in the page on balanced number partitioning . The (sum,sum) objective is the sum of weights of all items in all subsets, where the weights in each subset i are computed by the weight-function of matroid i .
Another generalization of cardinality constraints is as follows. The input items are partitioned into k categories. For each category h, there is a capacity constraint k h. Each of the m subsets may contain at most k h items from category h. In other words: all m subsets should be independent set of a particular partition matroid. Two special ...
In SQL (Structured Query Language), the term cardinality refers to the uniqueness of data values contained in a particular column (attribute) of a database table. The lower the cardinality, the more duplicated elements in a column. Thus, a column with the lowest possible cardinality would have the same value for every row.
The cardinality of the natural numbers is denoted aleph-null (), while the cardinality of the real numbers is denoted by "" (a lowercase fraktur script "c"), and is also referred to as the cardinality of the continuum.
Cardinality constraints are expressed as follows: a double line indicates a participation constraint, totality, or surjectivity: all entities in the entity set must participate in at least one relationship in the relationship set;
The problem of maximizing a monotone submodular function subject to a cardinality constraint admits a / approximation algorithm. [21] [22] The maximum coverage problem is a special case of this problem.
Cardinality bounds can be used in the body of a rule as well, for instance: :- 2 { p , q , r }. Adding this constraint to an Lparse program eliminates the stable models that contain at least 2 of the atoms p , q , r {\displaystyle p,q,r} .